This invention relates to ultrasound displays, and more particularly relates to such displays in which a region of interest can be identified.
Most state-of-the-art ultrasound scanners feature one or more zoom display modes. In a basic zoom mode, a region of interest (ROI) is selected via trackball control, which is magnified to the full display image area when a zoom button is pressed. The ROI magnification can be implemented simply by interpolating up the video image in the backend processor of the scanner. While this enlarges the display area for the ROI, it does not improve the fundamental resolution of the anatomy.
An xe2x80x9cacoustic zoomxe2x80x9d is often used to provide a higher resolution zoom image. This is accomplished by increasing the data bandwidths (not just display pixel count) in the lateral and axial dimensions. In accordance with standard image sampling theory, an increased spatial bandwidth in either dimension generally requires a corresponding increase in the data sampling rate. For ultrasound systems, this means that the vector density, axial sampling rate, and their corresponding filter bandwidths, should always be linked to the image display size. Examples of specific implementations are taught in U.S. Pat. No. 5,509,415 entitled xe2x80x9cMethod for reducing vector density based on image size,xe2x80x9d and in European Patent No. EP 0707219B1 entitled xe2x80x9cUltrasound diagnostic imaging with enhanced zoom.xe2x80x9d For an acoustic zoom, higher lateral display resolution is often obtained by increasing the beam vector density (e.g. 2xc3x97) within the ROI. An increased axial display bandwidth (resolution) usually involves reducing the post-detection low pass filtering before scan conversion.
In either display or acoustic zoom, the entire image display area is used to display the enlarged ROI image. The limitation is that the user loses sight of the original xe2x80x9cbig picturexe2x80x9d which often contains useful contextual information that may help interpret detailed anatomical information in the zoom image.
A number of solutions have been developed to provide a reference image in zoom mode. A commonly available method is to keep in the monitor display a highly reduced version of the original image with the ROI highlighted for easy reference. This reference image may or may not be frozen.
Another relatively new xe2x80x9cpicture-over-picturexe2x80x9d (POP) display zoom for B-mode shows a magnified (e.g. 2xc3x97) view of an ROI box over the original full-size B-mode image (to be referred to as the reference image hereafter). This is adapted from the sub-window display capabilities of modern television sets. One important aspect of the POP mode is that both the reference image and POP zoom display are live images. The ROI box can be moved anywhere in the reference image via trackball control. The POP display zoom box is automatically positioned within the image display area such that it does not obstruct the smaller ROI box in the reference image. The advantage of the POP display zoom is that the live and magnified image can be generated instantly simply by interpolating up the ROI in the reference image; i.e., it is a pure post-processing operation. The disadvantage of such a display 2xc3x97 zoom is that the POP image often looks blurry compared to the ROI in the reference image.
In an acoustic zoom mode, the reference image is either not available (zoomed-up image takes up the entire display), or frozen and reduced in size. To provide a live acoustic POP zoom (with increased vector density), and a live reference image, the scanner would need to alternate between acoustic zoom firings and reference image firings, which would likely reduce the image frame rate.
U.S. Pat. No. 5,873,830 (Hossack et al., issued Feb. 23, 1999) describes a technique which consists of using different imaging parameters for an ROI within a larger background image. The imaging parameters may be optimized to increase resolution or frame rate etc. This is not to be confused with a zoom feature because the ROI is not magnified for display. The present invention addresses the problems which are unresolved by the above-described techniques and provides a high resolution enlarged image which solves these problems.
The preferred embodiment is useful in an ultrasound scanner in order to create a reference image derived from scanning a subject under study with ultrasound waves and to simultaneously display an enlarged image corresponding to a selected region of interest of the reference image. In such an environment, the preferred embodiment generates received signals in response to ultrasound waves backscattered from the subject, preferably by use of a receive unit. First display signals corresponding to the reference image are generated in response to the received signals, preferably by a first logic unit. Second display signals corresponding to the enlarged image are generated in response to the received signals independent of the generating of the first display signals, preferably by a second logic unit. The reference image is displayed in response to the first display signals, preferably on a display, and the enlarged image is displayed in response to said second display signals, preferably on the display.
By using the foregoing techniques, an enlarged image can be displayed with a reference image with a degree of spatial resolution and rapid frame rate previously unattainable.